Field
The present disclosure generally relates to wireless communication systems and, more specifically, to improving the efficiency of power amplifiers therein.
Description of the Related Art
Power amplifiers are widely used in various communication networks to set the transmission power level of an information-bearing signal transmitted by a device. For example, power amplifiers are used to set the pulse energy emitted by pulsed lasers in optical communication networks. Power amplifiers are also used in the radio frequency (RF) front end components of wireless carrier network devices—such as base stations, repeaters, and mobile devices—to set the power level of a signal transmitted through an antenna. Power amplifiers are also used in local area networks to support both wired and wireless connectivity of servers, computers, laptops, and peripheral devices.
Managing the operation of a power amplifier is often of particular interest in mobile devices. The efficiency of a power amplifier is often a leading factor in the efficiency of a RF front end, and in turn, battery life of a mobile device. Envelope tracking can be used to improve power amplifier efficiency. Envelope tracking includes adapting the voltage supply level provided to a power amplifier in relation to the envelope of the RF signal amplified by the power amplifier. In other words, the voltage supply level provided to a power amplifier increases in response to increases of the envelope of the RF signal. Likewise, the voltage supply level decreases in response to decreases of the envelope of the RF signal. Having the voltage supply level track the envelope of the RF signal reduces the peak-to-average voltage drop ratio across the power amplifier, and in turn, reduces the current drawn by the power amplifier. Envelope tracking is particularly useful in reducing the current draw within RF signal troughs, during which current draw by the power amplifier usually peaks.
A coupling capacitor is typically used to isolate the DC voltage level of the envelope tracking circuitry from the DC voltage supply of the power amplifier. However, because of the finite size of the coupling capacitor, near-DC low frequencies are also typically blocked by the coupling capacitor along with the DC voltage level of the envelope tracking circuitry. As a result, the efficiency of a power amplifier at near-DC low frequencies cannot be improved by envelop tracking using known methods and circuit arrangements because of the finite limitations of coupling capacitors.